(1) Field of the Invention
This invention generally relates to a control system located at a first, or reference, site for guiding a steerable object from that site toward a contact or target. More specifically this invention relates to such a control system that guides the steerable object to a predetermined final approach course to the contact.
(2) Description of the Prior Art
Real time control systems based upon sensory inputs find application in air-, land- and underwater-based vehicles. If the range, course, speed and bearing of a target are known, a "target intercept" control mode can be used. In the target intercept control mode, a control system predicts the trajectory of the target and directs the torpedo to an anticipated intercept point. A control system operating in a "target pursuit" mode directs the torpedo so that it always points toward the target. In a "beam riders" control mode the control system directs the torpedo along a bearing between the submarine and the target. U.S. Pat. No. 5,319,556 to Bessacini (1994) discloses adaptive trajectory apparatus for selecting one of these control modes based upon information available during each update cycle for a given situation. U.S. Pat. No. 5,436,832 to Bessacini et al. (1995) discloses guidance system based upon beam rider control using fuzzy control logic. U.S. Pat. No. (Ser. No. 08/498,810 filed Jul. 6, 1995) by Bessacini et al. for a Fuzzy Controller for Acoustic Vehicle Target Intercept Guidance discloses one version of a target intercept guidance system.
The foregoing control systems direct a steerable object, such as a torpedo, to intercept a contact at an arbitrary angle. However many contacts have different sensitivities to noise in different directions. For example, a target constituted by a moving submarine is least likely to detect a torpedo approaching along its course line from the stern. The noise that the contact produces through propeller and other noise tends to be masking and minimize the chance of such detection. Moreover if a torpedo approaches the stern of a submarine it is more likely to cripple the submarine by damaging the propellers and or steering mechanisms with a minimal torpedo detonation. It is also characteristic of such an approach that the torpedo tends to move away initially from the bearing between the launching vehicle and the contact thereby to minimize any chance that the torpedo or other steerable object will mask signals used to provide contact state.
Such a trajectory, called a "tail chase" trajectory is highly desirable. Prior fuzzy controllers have the ability to achieve such a trajectory, but only if a launching vehicle is properly positioned relative to the contact at the time of launch. Other classical approaches that produce a target pursuit trajectory are more likely to produce a tail chase trajectory. However, in actual practice it has been found that, under certain circumstances, turn rates required by such classical techniques have not been attainable. Consequently the classical methods do not produce a tail chase trajectory as a standard final approach to a target. Consequently none of the control systems including those implemented in accordance with classical approaches or the foregoing Bessacini et al. patents (and applications) incorporate any mechanism for readily producing a tail chase trajectory.